Often, one needs to physically connect separate pieces of optical fiber to create a complete optical path for a signal. To do this, the separate fibers are connected by a splice. There are various ways to splice optical fibers. One way of splicing uses an arc-fusion technique. This technique entails stripping approximately 1.5 cm of the jacket from an optical fiber. The stripping step can be performed using an acid or heat-stripping process. The fiber is then cleaved with a fiber cleaver to approximately 0.5 cm, and cleaned in an ultrasonic cleaner. Finally, the fiber is placed in fiber-splicer chucks for alignment and fusing. The arc fusion technique melts the tips of the two fibers together.
Typical problems with splices include signal loss across the splice, environmental degradation of the bare optical fiber, and physical weakness at the splice point. Signal loss can arise from a number of causes, including mismatch between the profiles of the fibers at the joint, misalignment of the fiber cores due to core concentricity error, poor mechanical alignment due to lateral offset, separation, or tilt, and core deformation due to the fusion technique employed.
Environmental degradation of optical fiber can occur when unjacketed fiber is exposed to air, as might happen when protective jackets of unattached fibers are stripped prior to fusing. The fiber degradation reduces the period of time for which the fiber operates at the expected performance level.
Additionally, the splice point is considered a weak point along the fiber, making the fiber at this point more susceptible to cracking or breaking if handled the way one would handle a non-spliced fiber. Specifically, spliced fibers typically cannot be bent in the same way or to the same degree as non-spliced fibers because the stress from bending at the splice point can sever the fiber segments at the splice.
To alleviate the problems associated with splicing, it is known in the art to place a rigid splint around the optical fiber at the splice point. The rigid splint protects the optical fiber against environmental degradation by creating a relatively snug covering over the fiber. Additionally, the rigid splice protects the optical fiber against bending at the splice point, thereby protecting the splice point against mishandling.
There are several examples of rigid splints known in the art. One example of a rigid splint is made by Fujikura, and is called the PF-3 Splice Protection Sleeve. This sleeve has a three-part design, including a hot-melt type adhesive inner tube and a rigid reinforcement member enclosed in a cross-linked polyethylene heat shrinkable outer tube. Another such example of a rigid splint is the butterfly plastic ULTRAsleeve splint. The ULTRAsleeve is manufactured by using an acrylic foam closed cell tape to seal against chemical and environmental conditions for long-term applications. The rigid plastic housing consists of two halves that fold along a hinge (similar to a door hinge). The splice is placed inside the plastic housing; the locks on the sleeve keep the rigid protection cover from opening, and compresses the acrylic foam to provide a hermetic seal.
Unfortunately, these rigid splints create problems, inter alia, with handling the spliced optical fibers. For example, when creating circuits, it is very difficult, if not impossible, to place a spliced wire into an optical tray that has many curves. If one desires to place the fiber in such a tray, or if one desires to spool the wire, one must guess the proper length of the fiber so as to position the splice in a predetermined straight-line storage area on a fiber-optic tray.
Another problem with a rigid splint is that , because they must hug closely the exposed fiber to prevent environmental damage, they often physically damage the fiber when they are applied. For example, when one applies the butterfly plastic ULTRAsleeve splint, one can damage the fiber when the splint is mechanically crimped into place around the splice.
Additionally, rigid splints can damage a fiber at the point the fiber exits the splint. If a fiber bends at the point where it leaves the splint, it is possible to either kink the fiber, thereby increasing physical strain and degrading signal transmission, or bend the fiber to the point where it breaks.
Historically, neither the need nor the knowledge existed for creating strong flexible splices. With the recent explosion in the use of optical communications, however, particularly with regard to circuit design, a growing need exists for both strength and flexibility with regard to an optical fiber splice without significant signal loss.